1. Field of the Invention
This invention relates to a pneumatically-operated water control valve suitable for use in semiconductor integrated circuit (IC) device manufacturing plants.
2. Description of the Related Art
It is common knowledge that IC device manufacturing plants require a great amount of pure water in the wafer manufacturing processes.
Pure water for IC manufacture is produced by a water purification plant and supplied to the IC manufacturing plant through a piping system. The piping system generally forms a closed loop which comprises a first main pipe for supplying pure water from a water purification plant to an IC plant and a second main pipe for returning unused pure water from the IC plant to the water purification plant. Air-operated water control valves are conventionally used at use points of the piping system to distribute pure water to desired sections of an IC manufacturing line. When the water control valve is in a closed condition, the unused pure water returns to the water purification plant to purify it to a desired purity. The conventional water control valve has in it a bellows which prevents pure water from contacting the piston shaft in the air actuator and is made of, for example, TEFLON (Trademark of Du Pont polytetrafluoroethylene).
In general, a lubricating oil is applied on the surface of the piston shaft to provide for its smooth movement. A long use of the water control valve sometimes results in a crack in the bellows due to fatigue failure. Such failure would result in oil leakage causing serious damage to the whole pure water piping system and sudden degradation of the purity of the pure water, resulting in a poor yield of IC devices.
Since a prior art water control valve with an air-operated actuator has an opening providing communication between the inside of the bellows and the atmosphere, a bellows failure can be detected by observing pure water leaking from the opening.
However, it has been difficult to find the belllows failure before contamination of the pure water piping system.